Since this is more or less my 'forte' when it comes to World War II studies and especially the Eastern Front is where my concentration lies, specifically 1941, I was very pleased to get my hands on a copy of this book even before it was published (thanks to my history professor at my University). Overall it was a solid effort on the part of the author to show how much information Stalin, GRU, and in effect the Soviet Union was receiving from abroad. From Eastern to Western Europe and the US, embassies and personnel were sending information confirming the time of the invasion and detailing what the invasion itself would encompass or simply denying it as part of a German deception campaign.
When viewing this information we can see that much of the data that confirmed the invasion was in fact correct while many details were not. Bottom line being that the idea that an invasion was going to occur was most definitely right but the dates being attributed to the invasion were not.
The first messages began to arrive soon after December 1940 when Hitler has first through up of the invasion, but they were in effect useless since no troop movements had begun. The first thoughts coming into Stalin's mind were probably that it couldn't be true since Germany was still at war with England and Hitler would never make the mistake that was made in World War I when a two front war was fought and lost by Germany.
The US was also one of the first to warn Stalin but in the end why should Stalin trust them? Or Great Britain who also tried to warn him? They had interfered in the Russian civil war, sent their troops to Russian lands to kill Red Army men, and now when only England was standing up to Hitler and Germany would it not suit England's interests to get the USSR on her side? This is one thing that has to be kept in mind, most messages from foreign sources like these were ignored, even worse if they were substantiated by other sources it simply made it seem as if this information was planted.
Later on during one or two months before the invasion began an avalanche of information was forthcoming about Germany's intentions from every corner of the globe. Yet this is where the author makes a mistake, he does not in fact show all German deception that was focused on keeping the Soviet uninformed about their plans nor does he show some of the contradictory information coming in from the very same Soviet agents and sources that said Germany would attack. This is most definitely a lot to grasp and keep in mind. One example of the authors omission is from that famous spy Sorge in Tokyo, a few days before the invasion he sent a message saying "Germany might not attack or if it does it'll be at the end of June" this was sent on June 17th. I have in fact collected some of the volumes that Murphy based his work on and much of the information found in them he has omitted, this being just one example. Although in the end one cannot blame him for this, there is a wealth of information and a limited amount of space to present it all in within Murphy's book. So I commend him for what he's done in at least bringing this topic to light in English.
Now going back to some of the first details that were surfacing about the invasion, their estimates were March, and then later on mid May. March was seen as a joke since this was right after winter and before the rasputitsa would begin, thus Germany would simply be bogged down in the mud. May was more feasible but when it came and went and nothing happened, why should Stalin even consider that if they were wrong once they'd be right the next time? Mobilizing a country, any country, is a lot of work and at that time for Stalin mobilization meant war. The reasons for why he thought Hitler would first make demands are explained in the book, which I give the author credit for finding out, as well as the fact that Golikov the Chief of GRU was hiding a huge amount of information from Stalin and supplying him with what he thought Stalin wanted to see and hear.
This of course made it much harder for Stalin to believe the few pieces of information that might have slipped through or he was told about by others which did in fact confirm the invasion. Usually his estimation of what Germany would do rested with the disinformation Germany was supplying throughout Europe to keep the USSR in the clouds vis a vis German intentions toward it. Also keep in mind that when information started to pile up about German invasion plans, who would believe that such a crucial event would be massively broadcast throughout the world? It would have been believable from a few sources, but from dozens all over the world parroting the same thing? It couldn't be true, it was a deception by the British and Americans to get the USSR into war with Germany! I'm sure I'm forgetting much that was addressed and was forgotten about in this book but overall it is a good investment for those who want to understand something of why this was a surprise to Stalin and what kind of information he was receiving.